As an onboard light source, longer-life, maintenance-free LEDs have been spread as a substitute for conventional tungsten lamps. Since the LEDs have longer life and are able to maintain required brightness with smaller power and stable brightness with simple control that supplies a constant current, they are appropriate to an onboard light source. For the same reason, LEDs are rightly used as a light source other than the onboard light source.
Incidentally, the brightness of the light an LED emits is mainly determined by the current flowing through it. In addition, as for LEDs corresponding to lighting functions such as those of the antidazzle lights and running lights of headlights and those of the taillights and sidelights of a rear combination lamp, LEDs suitable for these functions are selected. Accordingly, although the current flowing through LEDs of a single illuminator varies depending on the individual functions, it is preferable for a lighting device to collectively supply the currents to the LEDs with the individual functions. As configurations of a lighting device that turns on a plurality of LEDs with different currents at the same time, Patent Documents 1-3 are proposed, for example.
An LED lighting unit of the Patent Document 1, which emits white light by turning on red, blue and green LEDs, has the red, blue and green LEDs that have different applied currents and are arranged in parallel with respect to a power supply, and has current adjusting circuits (current limiting resistors) for them, respectively.
A lighting unit of the Patent Document 2 has two types of LEDs that have different applied currents and are connected in series, and uses a transformer having the principal secondary winding and subordinate secondary winding. The transformer supplies the LEDs connected in series with the current output from its principal secondary winding (principal current) and supplies a part of the LEDs connected in series with the total current of the principal current and the current from the subordinate secondary winding (subordinate current), thereby increasing the brightness.
A lighting unit relating to the Patent Document 3, which simultaneously turns on two types of LEDs that have different forward voltages and are connected in series, comprises a current control unit connected in parallel with the LEDs with higher forward voltage. The current control unit adjusts the forward current flowing through the LEDs with the higher forward voltage, thereby keeping the balance between the power supplied to the LEDs with the higher forward voltage and the power supplied to the LEDs with lower forward voltage.